The invention relates generally to power-driven conveyors and, more particularly, to modular-belt conveyors using shoes with rollers as holddowns and in returns.
Modular plastic conveyor belts are widely used in many conveying applications. These belts are constructed of belt modules arranged side to side in rows that are connected together end to end at hinge joints by hinge rods into endless belt loops. Because these belts are most commonly made of a slick, plastic material, they exhibit relatively low friction compared with flat rubber belts. In a typical layout, the belt loop is trained around drive and idler sprocket sets at each end of a conveying path. Articles are conveyed atop the belt supported along an upper carryway. The belt returns along a lower returnway. To minimize the maximum sag of the belt in the returnway, return shoes or rollers are often used. Return rollers typically extend across the width of the belt at selected positions along the returnway. While return rollers work well with belts having a flat outer surface completely or largely devoid of protruding elements, they can damage or interfere with flights, sideguards, and other upstanding structures on many modular belts. For these belts, shoes, which extend over only a portion of the width of the belt, are used. A typical shoe presents a curved support or bearing surface to a flat longitudinal lane of the outer surface of the belt. Most often, these lanes, devoid of upstanding elements, lie along the side edges of the belt, but lanes may exist along interior portions of the belt. (Shoes are also used along the carryway as holddowns in elevating conveyors at the transition of the belt from horizontal to incline.) In most cases, the sliding friction between the shoes and the outer surface of the plastic belt as it rides over the shoe is tolerable. But, in some applications, the friction between belt and shoes may require a stronger belt or a more powerful conveyor drive motor.
Thus, there is a need for a limited-width, low-friction return or holddown support for a modular plastic conveyor belt.